( Reaffirmed 2012 ) IS : 6693 - 1972 Indian Standard SPECIFICATION EBONITE Rubber Chnirn2an DR D. BANERJ~IZ FOR Products Sectional Committee, R@resenting CDC 6 National Rubber Manufacturers Ltd, Calcutta; and Association of Rubber Manufacturers in India, Calcutta Members SHKI A. T. BASAK Directorate General of Supplies & Disposals SHRI V. K. B~ASKARAN NAIR Rubber Board, Kottayam SHRI K. C. ANANTH ( Alternate ) SuRI S. K. BOSE National Test House, Calcutta SRR~ A. GHOSH ( Alternate ) SHRI D. K. CIIATTERJ~E Alkali & Chemical Corporation of India SHRI S. S. CHWRA Export Inspection Council of India, Calcutta SHRI K. M. BIJLI ( Alfernate ) SHRI B. fl. DALAL Ministry of Defence ( DGI ) SI~RI M. KUMARAN( Altmate ) SHRI S. L. GANDHI Ministry of Dcfence ( DGI ) SKRI M. G. BHARCAVA ( Alternate ) SHRI G. C. JAIN Hindustan Steel Ltd, Ranchi SHRI 0. N. KOHLI Railway Board SHRI LALIT MOHAN,JAMNADAS Cosmos India Rubber Works Pvt Ltd, Bombay SHRI PCJLIN L. KINARIWALA ( Alternate ) SHRI S. V. LATHIA Lathia Rubber Manufacturing Co Pvt Ltd, Bombay SARI D. P. LATIIIA ( A/term& ) DR S. K. MATTIIAN Madras Rubber Factory Ltd, Madras &RI K. J. A~RAAAM ( Alternate ) All India Rubber Industrirs Association, Bombay; DR K. N. MODAK and Indian Rubber Manufacturcls Research Association, Bombay SIIRI S. R. SENGUPTA ( Aliernale ) All India Rubber Industrirs Association, Bombay Dunlop India Ltd, Calcutta SHRI S. MUKHERJEE SHRI I'. N. S. MYER ( Alternate ) Bata Shoe Co Pvt Ltd, Calcutta SHRI S. C. NANDY &RI 13. R. PAN~IT Bayer ( India ) Ltd,, Bombay Synthetics & Chemicals Ltd, Bombay &RI M. M. PA.I.BL Indian Oil Corporation Ltd, Bumbay SHRI K. RAJOOPAUL 13~ A. SEEWARAMIAH Directorate General of Technical Development DR N. V. C. RAO ( Altcrnnte ) ( Continued on jage 2 DR S. K. RAY ( Alternate ) Calcutta Ltd, ) INDIAN MANAK STANDARDS BHAVAN, INSTITUTION ZAFAR MARG 9 BAHADUR SHAH NEW DELHI 1 IS : 6693 - 1972 ( Continued from page 1 ) Representing All India Automobile Association, Bombay & Ancillary Industries Members SHRI D. D. TALWALKAR SHRI R. M. KHALADAR ( Alternate ) Dirrctor General, IS1 ( Ex-ojicie .Qfember ) SHRI D. DAS GUPTA, Director ( Chem ) Secretary SHRI SATISH CHANDER Deputy Director ( Chem ), ISI General Cunuener DR Rubber Products Subcommittee, CDC 6 : 4 M. L. BHAUMIK Members National Rubber Manufacturers Ltd, Calcutta Bengal Waterproof Works ( 1940 ) Pvt Ltd, Calcutta National Test House, Calcutta Alkali & Chemical Calcutta Corporation of India Ltd, SHRI A. BOSE SHKI R. S. ROY ( Alternate) SlIRt S. K. Soslc SHRI A. GH~SH ( Alternate ) SHRI K. R. SOSHAI>RI (Alternate) SHRI D. K. CHATTERJEE National Safety Council, Bombay Ministry of Defence (DGI ) SHRI B. H. DALAI. SHRI G. C. CHAKRAVARTY I Alternate ) Central Water & Power Commission, New Delhi DIRECTOR( TRANSMISSION ) . SHRI S. P. JAIN (Alternate) Railway Board SHRI C. D. DIXIT Hindustan Steel Ltd, Ranchi SHRI G. C. JAIN SHRI A. K. GHOSH ( Alternate) Common Facility Service Centre, Changanachery SHRI K. A. JOSE Lathia Rubber Manufacturing Co Pvt Ltd, Bombay SHRI S. V. LATIIIA SHRI D. P. LATHIA ( Alternate ) Dairy Development Commissioner, Government of SHRI N. LAXMINARAYAN Maharashtra, Bombay Indian Rubber Industries Association, Bombay DK K. N. MODAK SHRI S. V. LATHIA ( Alternate ) Rubberex Industries Pvt Ltd, Bombay SHRI M. M. PATEL SIIRI K. C. SHAH ( Alternate) Synthetics & Chemicals Ltd, Bombay SHRI M. M. PATEL Swastik Rubber Products Ltd, Poona SHRI V. D. PENDSE SIIRI D. D. TALWALKAR ( Altcrnote ) DR N. V. C. RAO Directorate General of Technical Dcvelonment SIIRI C. R. INAMDAR ( Alternate ) SHRI R. N. RAY Dunlop India Ltd, Calcutta SHRI B. K. DAS ( Alternate ) BRIG P. R. CIIAUIIAN 2 IS : 6693 - 1972 Indian Standard SPECIFICATION EBONITE 0. FOREWORD FOR 0.1 This Indian Standard was adopted by the Indian Standards `l~rtitution on 30 October 1972, after the draft final&d by the Rubber ~O~UCLS Sectional Committee had been approved by the Chemical 1Avision Council. 0.2 Requirements for two t.ypcs of ebonite, namely, unloaded :md loaded, have been covered by this sta~~dax,l. Unloaded ebonite is black in colour while loaded ebonitcs are usually supplied in red or brown colour to distinguish it from other types. Impact test has not been included and its introduction would be considcrcd at a later stage. 0.3 Considerable assistance: has been drawn ' tiolls in the preparation of this standard: BS BS 234 : 1971 purposes. from the following for publicaelectrical purposes. Loaded and unloaded ebonites British Standards Institution. ebonites 3164 : 1959 Loaded and unloaded British Standards Institution. for general 0.4 This standard contains clauses 4.1.1 to 4.1.3, 4.2.1, 4.2.3, 4.3.1, 4.5 and 4.6 which call for agreement between the purchaser and the supplier. 0.5 For the purpose of deciding whether a particular requirement of this standard is complied with, the final value, observed or calculated, expressing the result of a lt.st or analysis, shall be rounded off in accordance The number of significant places retained in lhc with IS : Z-1960". .ounded off value should be the same as that of the specified value in this iandard. 1. SCOPE 1.1 This standard and tests sampling mouldings. *R&S for rounding prcscribcs the for ebonite in requirements and the methods of the form of sheets, rods, tubes and ). off nulncrical values ( mirrd 3 IS :6693 - 1972 2. TERMINOLOGY 2.0 For the purpose 2.1 Cross Breaking bending a bar shaped of this standard, the following definitions shall apply. by Strength -The load required to fracture test piece of given rectangular cross section. breakdown strength to produce a discharge 2.2 Electric Strength-The thickness of material required the material. in kilovolts per unit through the body of 2.3 Permittivity - The ratio of the capacity of a condenser having the material as diclyctric to the: capacity.of a similar condenser having air, or being made t more precisely vxuum, as dielcc:irtc, the measurements alternating current. total deformation of bar shaped test piece 2.4 Plastic Yield -The stressed under ,givcn conditions at a given lempcrature for a given time. 2.5 Loss Tangent - 1%~ ratio of the power loss ( watts ) in the material when used as the dielectric of a condenser to the total power transmitted througlr the condenser. 3. TYPES 3.1 This standartl covers two types, material depending upon the physical 4. REQUIREMENTS 4.1 Material and Workmanship namely, Type characteristics. 1 and Type 2 of the 4.1.1 Ebonite shall be manufactured from rubber and sulphur with or without the addition of suitable compounding ingredients of such value and quality that the finished product complies with the requirements Any special characteristic other than those specified in this standard. prescribed in this specification which may bc desired for specific applica, tion shall be specified by the purchaser as they may infiuence the choic of tlJe ingredients used. 4.1.2 All sheets shall be flat and free frown irregularities and shall normally Ix supp1ic.d witlr the finish ( such as matt, srrlooth or foil finish ) as specified by the purchaser. 4.1.3 Rods and tubes shall be straight and free from cracks and flaws. They shall normally be snpplicd with a rough ground finish, a fine ground or polished finislr when specified by tire purchaser. $1.4 The material shall be free from embedded 4 metallic particles. IS : 6693 - 1972 4.1.5 Machining -The materia1 shall be tapped, cut and machined without difficulty, reference sample approved by the purchaser. capable of being and shall conform `drilled, to the 4.2 Dimensions and Tolerances 4.2.1 Sheets -The preferred dimensions for sheets are those given below. When material is reqllired in other sizes, the cominal dimensions shall be the subject of agreemrn t between the purchaser and the supplier. Length and Width 900 x 600 mm. 900 x 450 mm 600 x 600 mm 4.2.2 Thickness Any thickness from 1.5 to 50 mm inclusive dimensions for rods are: PreJerred Length diameter 100 mm lm 0.6 III Rods - The preferred Rod Diameter From 3 to 60 mm specified Above 60 mm and up to specified diameter 4.2.3 Tzrbes - Unless olhrrwisc spccific,d, tubec of under 40 mm diameter The Icngth of` tllbrs of over shall bc supplied in Ien,& o!` one mctrc. 40 mm diameter shall IX 1)~ agreement between the purchaser and the supplier. 4.2.3.1 to between 4.3 The diameters and wall thicknesses the purchaser and the supplier. on Dimensions of tub-s shall be as agreed Tolerances 4.3.1 Sheets, Rods and Tubes -The thickness of sheets, the diameter of rods alld the internal ;md oxtcrnal diameters of tubes shall not differ from the spclcific,d values by rncr:~: than the appropriate tolerance given in Tables 1, 2 and 3. Tl,r difE,r!>ncc: between the maximum and minimum wall thickness of any tt~bc, m~*;:sured near each end, shall not exceed the appropriate value given in Table 4. 4.3.1.1 When malrrial is reqllired in sizes not provided for in Tables 1 to 4 or with finishes other than rough-ground or fine-ground in the case of rod or tube, and foil lirlisll ii1 the case of sheet, the tolerances shall be as agreed to bctwccn t11c pur~~h;~sc;_and supplier. 4.4 Plastic Yield-When tllrec test Ilieccs are tested in 3 Istir: yichld shall not cxcccd with App<*ndix A, t11c. ~VWZL;;C pa.., 3 mm at 55°C for `I'ypC 1 and 3 ml)1 at 70°C for Type 2. accordance more than 5 IS : 6693 - 1972 TABLE 1 DIMENSIONAL TOLERANCES FOR SHEETS ( Claurc 4.3.1 ) All dimensions in millimctres. SPECIFIED THICKNESS h-____-~ TOLERANCE OH THICKNESS -------Above Up to and Including (2) 1.5 2.5 3.0 10.0 20.0 30.0 50.0 (1) 1.5 2'5 3.0 10.0 20.0 30'0 (3) + 0.08 & 0.10 f f f f f 0.13 0.25 0'40 0.50 0.65 TARLE 2 DIMENSIONAL TOLERANCES FOR RODS (Ctause 4.3.1 ) All dimensions in millimetres. SPECIFIED DIAMETER * __7 TOLERANCE ON DIAMETER C---------*-____---___~ r Above Up to and Including Rough-Ground ~----h---, Plus (3) 0.2 0.3 0.5 Finish Minus (4) 0.00 0.00 0.00 Fine-Ground r--_-h___ PIUS (5) 0.05 0.05 - Finish Minu? (8) 0.05 0.05 supplier (1) 3.0 20.0 30.0 50.0 (2) 20.0 30'0 50.0 - By agreement between the purchaser and the IS : 6693 - 1972 TABLE 3 DIMENSIONAL TOLERANCES FOR TUBES ( Clausa 4.3.1 ) All dimensions in millimetres. EXTERDIAMETER ~---h_-.--.-) up to Above and Including SPECIFIED NAL INTERNAL DIAMETER c-_---~ Plus Minus EXTERNAL DIAMETER ~___---__h_-___---~ Fine-Ground Rough-Ground Finish Finish r___h_--y r___&.--~ Minus Plus Minus Plus (5) 0.2 0.2 0.2 0.3 0.5 (6) 0.00 o*oo 0.00 0.00 0.00 (7) 0'05 0.05 0.05 0'05 (8) 0.05 0.05 0.05 0.05 - (1) 6.5 13 19 30 (2) 6.5 13 20 30 50 (3) 0.08 0.13 0.20 0.00 0.00 (4.) 0.08 0.13 0.20 0.50 0.80 TABLE 4 MAXLMUM VARIATION IN WALL ANY ONE TUBE ( c[nuse 4.3.1 ) THICKNESS OF All dimensions in millimetres. SPECIFIED WALL THICKNESS r__--__h_---..-~~ MAXIMVM VARIATIONIN Above (1) 3.0 6.5 10.0 Up to and Including (2) 3.0 6,5 10.0 - r--------- WALL A-.-________~ THICKNESS Extruded Tube (3) 0.20 0.25 0.30 0'40 Tube Hand-Built from Calendered Sheet (4) 0.80 0.80 1.6 1.6 4.5 Cross Breaking Strength-When three test pieces accordance with Appendix A, the average cross breaking satisfy the following requircmcnts: Minimum proof load, kgf 7ype 6.0 1 are tested in strength shall Tj$Je 2 3.0 4.6 Permittivity and LOSS Tangent -The values of these two characteristics shall not exceed the following appropriate figure5 when determined at audio frequency or at radio frequency as given ir\ 7 IS : 6693 - 1972 Appendix A. Five samples are to be tested, out of which four test pieces shall withstand the-required specification. Unless otherwise specified, the permittivity and loss tangent shall normally be determined at audio frequency: Permittivity Loss tangent Pcrmittivity Loss tangent at audio frequency, at audio frequentiy, at radio frequency, at radio frequency, MUX Max 114~~ Max lryPe 1 3.3 0.008 3.3 O*OlO fiPe 2 3.8 0.008 3.8 0.012 4.7 Electric Strength Option'al Requirement - When five test pieces arc tested in accordance with the test method given in Appendix A minir;ltlm of four test pieces shall withstand the following appropriate test voltage without breakdown for one minute: 7ype 1 Electric Tjpe 2 30 strength, AND proof voltage, PACKING kV 40 5. MARKING 5.1 Each piccc of the material `shall be marked in a suitable position with: by the purchaser; and diameter; 21) the manufacturer's c) essential dimensions and d) the type. name or trade-mark; if required width, like length, thickness b) the month and year of manufacture, 5.1.1 Individual pieces of the material may also be marked with the IsI Certification Mark. NOTE- The use of the ISI Certification Mark is governed by the provisions of the Indian Standards Institution ( Certification Marks ) Act and the Rules and Regulations The ISI mark on products covered by an Indian Standard 7onveys made thereunder. the assurance that they have been produced to comply with the requirements of that standard under a well-defined system of inspection, testing and quality control which is devised and supervised by IS1 and operated by the producer. IS1 marked products ale also continuously checked by IS1 for conformity to that standard as a further Details of conditions under which a licence for the use of the 1SI Certifica_ safeguard. tion Mark may be granted to manufacturers or processors, may be obtained from the Indian Standards Institution. 5.2 The material the supplier. 6. SAMPLING shall be packed as agreed to between the purchaser and 6.1 For the purpose of ascertaining standard, the method of sampling given in Appendix R. conformity and criteria of the matt:rial to this for conformity shall 1~~ as e IS : 6693 - 1972 7. TEST METHODS 7.1 The material shall be tested as prescribed in Appendix A. For pecmittivity and loss tangent it shall be clearly indicated as to whether the test is to be carried out at audio frequency or at radio frequency. APPENDIX (h7uses TEST 4-l. PLASTIC YIELD METHODS A 4.4 to 4.7 ) A-l.1 Outline of the Method -The test piece is measured after subjecting conditions. total deformation of a bar shaped it to a specified load under specified A-1.2 Apparatus -The apparatus shall consist of a clamp for mounting the test piece as a cantilever together with a stirrup for applying the load ( see Fig. 1 ). The stirrup shall he of such shape that it will rest in the notch of the test piece and distribute the load uniformly across its width. The mass of the stirrup and of any other a(tachmcnt ( for example, scale pan pointer) shall not exceed 9 g. A wei@t shall be provided for attaching Lo the stirrup so that the total appkd load including the mass of the stirrup is 180 f 1 g. k------A- FIG. 1 A-l .3 Procedure PLASTIC YIELD TEST PIECE A-1.3.1 Test Piece-The test piece shall bc a bar 85.0 & 0.5 mm long, 15.0 f 0.1 mm wide and 6.0 f 0.1 mm deep with a V-notch across one side 5.0 f 0.5 mm from the end ( see Fig. 2 ). 9 IS : 6693 - 1972 All dimensions in millimetres. FIG. 2 TEST PIECE A-1.3.1.1 Number the average of test pieces - Three test pieces shall be tested and of 3 results shall be taken as the plastic yield of the material. A-1.3.2 Conditioning of Test Pieces-Test shall not be carried out within 24 hours after vulcanization. Test pieces shall be protected from light as completely as possible during the interval between vulcanization and testing. A-1.3.3 lkmpcrature of 1 pst -The test shall be made at 55 or 70°C. A-1.3.4 Place the test apparatus in an oven and bring to within 1°C of the specified ternperaturc. Moilnt the lrst piece horizontally as a cantilcvcr in the clamp (sf'e Fig. 1 ), one end bring rigidly clamped so Ke\t the stirrup ill the notch. Rttacll the that n = 60 & 0.5 mm. mounting of the test piece as quickly 3s po_;aiblc ho that the ovc'n is not unduly cooled during the opcralion. Aft+:r the test piece has been in the oven for 15 minutes, n~casure tllc height of the stirrup relative to a datum Then attach the weight to the stirrup without disturbing the point. temperature conditions in the oven. Maintain the apparatlls and loaded test pieces for 6 hollrs f 10 minutes at the specified temperature. At the end of this time, with the load still in position remeasure the height of the stirrup. A-1.3.5 Result -Take the change in height yield of the test piece at the test temperature. A-2. CROSS BREAKING STRENGTH test piece is bent gradually for any fracture or wackiness. of the stirrup as plastic A-2.1 Outline of the Method -The applying specified loads and examined IJ,Y A-2.2 Apparatus - The apparatus shall consist of a clamp for mounting the test piccc as a cantilever toge:her with a stirrup for applying the load (bee Fig. 1 ). Th c s t irrup shall be of such shape that it will rest in the notch of the test piece and destribute the load uniformly across its width. A spring shall be inserted between the stirrup and load container to avoid IO IS : 6693 - 1972 shock loading. The total be approximately 0.5 kg. A-2.3 Procedure test piece shall be a moulded or machined bar, The test 6.0 rJs 0.3 mm square in cross section. across one side 5.0 f 0.5 mm from one mass of the stirrup, spring and container shall A-2.3.1 Test Piece-The 85.0 & 0.5 mm long and notched piece shall be end ( see Fig. 2 ). A-2.3.1.1 Conditioning oftest pieces-The test shall be carried out not Test pieces shall be protected from less than 24 hours after vulcanization. light as completely as possible during the interval between vulcanization and testing. The test pieces shall be conditioned at a temperature of 27 f 2°C for not less than 18 hours immediately before test. A-2.3.2 Number of Test Pieces of Test Four test pieces shall be tested. The test shall be carried out at a tempera- A-2.3.3 Temperature ture of 27 f 2°C. A-2.3.4 Clamp the test piece horizontally and normally to face the clamp as cantilever so that A = 60 5 0.5 mm ( see Fig. 1 ). The stirrup shall be placed in the notch with the spring and load container attached (A = distance bctwcen clamp and stirrup ). Increase !he load steadily at approximately 9 kg per minute to the specified value which includes mass to the stirrup, sprmg and load container. A-2.4 Results A-2.4.1 The test piece shall be deemed to have passed the test if it supports this load for one minute without fracture or cracking. A-2.4.2 A-3. At least three of the four test pieces tested, AND ) LOSS TANGENT shall pass the test. PERMITTIVITY FREQUENCY (AUDIO A-3.0 The loss tangent (tans ) and permittivity of a sheet after conditioning shall be determined by a suitable form ofapparatus, namely, Schering Bridge with Wagner Earthing Attachment. A-3.1 Apparatus * A-3.1.1 Electrodes-The test piece shall be provided with electrodes and a guard ring ( as shown in Fig. 3 ). The electrodes shall take on any of the following forms, preferably the one described in (a) which shall be used in any case for the referee method, in case of dispute: a) Graphite-This shall be applied, before conditioning, form of a colloidal suspension in water. It is convcnicnt II in the to dilute IS : 6693 - 1972 the graphite suspension with distilled water to the consistency of drawing ink, and then to draw the circular outlines of the electrodes and guard ring on the surface of the test piece with this ink, afterwards painting the appropriate areas with graphite suspension. Alternatively, the graphite may be applied by spraying with the help of suitable stencils. Metnl Foil-Discs of metal foil about 0.025 mm thick shall be applied after conditioning to the flat faces, using a very thin coating of petroleum jelly or silicone grease as adhesive. The foil shall be pressed and rolled on to the surface and smoothed down until all irre, c,. be c) The micromctcr incremental ing its micrometer head to condenser ~%f~ shall IX ?et by ad.just_ the approximate centrc of its range, 19 IS t 6693 - 1972 and the oscillator shall t.hen be tuned to the measuring circuit resonant frequency as indicated by peak galvanometer deflection. The frequency shall be checked by refcrencc to the oscillator If the calibration graph or table supplied witil the oscillator. frequency is not within the required rauge, the measuring circuit coil shall be changed. d) If the correct resonant frequency cannot be obtained as described under (c) above, then provided that the requirements given in A-4.2.2.1 are satisfied, the oscillator shall he set to the required frequency arid an auxiliary condcrrser shall be connected in obtaiued by parallel with the specimen condenser and rcsonaucc Care shol~ld he taken to varying this auxiliary condetrscr. In most casts this prcensure that the true reasonancc is found. sents no difliculty, but with close coupliu g betlveen the measuring circuit and the oscillator, the mcasurin, cr circuit may respond to a harmonic of tire oscillator frequcLicy. To guard against this, the effect of multiplying the oscillator frequency, say by 2, 3, 4 and & should be tried until the frequency giving the largest deflection is found. e) The valve voltmctcr controls ~1~11 be a~l~justrrl to ensure that the voltmeter reads zero when its input volt+ge is z2ro. The input voltage shall then be adjuvtcd to give approximately full scale deflection on the galvanomcter scale. ( 011 strfric: commrrcial models of this apparatus, this is achiC:vcd by moving the oscillator relative to the voltmeter and on other by varying the output from the oscillator. ) f) The micrometer head of the incremental condenser Mz shall be scrcwcd out until the galvanometer deflection is reduc1.d to a convcnicnt fraction 1 /q ( for example, 4 ) of t lit initial resonant reading and the micrometer readiug shall be noted. The micromctcr head of M? shall then bc scl,e\ved in until the galvanometc~r clcflcction attams its maximum va!u' ( aclliclr should have remained constant) and then screbvcd in furt1lc.r until the galvanometcr dcflcction is again rcd~~ced ii1 the ratio I/q. The reading of the microm?tcr head shall again bo noted, and the difi.rcnce in capaCitancc ( nci), ~(~1 `_ I (`5 . J~):ltli~l!g to the difference between these two readings of the micrometer, shall be obtained from the calibration graph or t:tble. the squnrc law relation of the valve voltmctcr, the ACr shall IC o!)t;&ecl for va111c:s or q z 2 and q = 5. `rile valtle oi' AC, ancl q = 5 should 1~1:twice Illat r(,t. q ; 2 if` the valve voltmeter s;llisfic.s the scl"are law rclal ion. Will1 specimens of high power factor it may not bc l>ossil)lc ;:o reclrlcc (1~1, galvanomctcr deflection to lhcsc fractions of the maximum deflection by d h) To check difference 20 IS : 6693 - 1992 In this case, means of the micrometer incremental condenser. the deflection shall be reduced to a convenient fraction ( say, # ) of its maximum value, where, for example, 4 .= 3/2, 5/4 or IO/g. The ratios of the two values of AC1 for any may be found from the following formula: two values of q (A Ct), (A Cl)`2 `V Qz-f2 percent The ratio of the two values of ACi shall be within of that corresponding to the square law relation. j) k) The mcasurirlg circuit shall be returned to resonance by means of the incrcment:J capacitor MX and the specimen shall be removed from betweell the plates of the spccimcn condenser Ml. The movable electrode of the specimen condenser M1 shall be adjusted until the measuring circuit is again in resonance, that is the capacitance lost by removing the specimen is restored by dccrcasirlg the distance bctwcen the condenser plates. The input voltage shall bc ad,jllsted, if required, to give approximately full scale dcllrzticoll. The specimen condenser scale reading shall be noted and used to obtain the corresponding capacitance, C,, from the specimen condenser calibration grapher table. The edge to the separation of the plates capacitaiicc:, Co, corresponding when the specimen is in the specimen condenser, shall be obt.air1c.d as described in A-4.4. The capacitance C, - C, ( = CS ) is equal to that of the specimen. The operation described in A-4.3.5(e) and A-4.3.5(5) shall be repeated using the same ratio 1 /q as before, and the correspondof the incremental condenser MS ing change, AC,, of capacitance shall be obtained. The square law relation ancc with A-4.3.5(11). may be checked at this stage in accord- m) n) A-4.4 Edge CorrectionFor sheet material in the form of disc, the edge capacitance, that is: capacitance rcprcsenting the portion of the electric field located round the edges of the plate electrodes, may be calculated from Kirchheff's formula: Edge capacitance, -72x where L), =;: diameter in mm of the plate electrodes, in mm of the plate electrodes, in mm of the specimen. 21 and Ce ( l@ 87-r n, ) (t-4-d) d' D L IOwe b r +-)og, t+ * d-3 1 t d = thickness = thickness 1s : 6693 - 1972 Experrencc wrth typrcal specimens has shown that, if the edge capacitance is derived from the formula on the assumption that the edge capacitance lies wholly in air, the error in the calculated value of specimen capacitance is not likely to exceed 2 percent for any ordinary specimen and in general the error will not exceed 1 percent. The following table gives the values of edge capacitance calculated in this way for different thickncss of specimen, for a value oft of 5 mm: Specimen ofThickness, d I.0 1-3 1.6 2.1 2.7 A-4.5 Calculation and Report hy either set of formulae Edge Capacitance, C I.5 1.4 I.3 I.2 1.1 A-4.5.1 Calculate tangent loss and permittivity given under (a) arid (b) below: a) Tinlgcrrt loss ( tan 8 ) = ac;; 2 (G-G) c, nco AG .2/q-- 1 Pcrmitlivity, h) `Tangent K = lSd( n;;; c, ) loss ( tan 6 ) = 2 C', d/4 - 1 Pcrmittivity, whcrc C'* = C8 Ci + K = `fi+jFIs F 02 144'd, in A-4.3.5 (b), Cl8 = Cl and AC, are obtained as described A-4.3.5(k), and A-4.3.5 (m); C, = edge correction 4 d = thickness as determined in A-4.4; = value of the fraction used in A-4.3.5(f) or A-4.3.5(11); condenser when in mm of the specimen; d, = separation of plates in mm of specimen the specimen is hetwccn the plates; and I), capacitance diameter in mm of circular plates of Specimen coridenser. and the change No.rB 1 - If there challge is a linear relationship between the micrometer reading of the incremental condenser AI*, the capacilancc 22 IS : 6693 - 1972 AC, - AC0 can be determined by multiplying the corresponding incremrntal condenser by aconstant corresponding to the capacitance change ( millimetres ) of the micrometer head reading. readings of the change per unit NOTE 2 - These formulae are derived on the assumption that the edge capacitance lies wholly in air. NOTE 3 -When measurements are required to the highest accuracy, then and A-4.3.5(g) have been carried out, immediately after operations A-4.3.5(f) operation A-4.3.5(f) shall be repeated; the reading obtained should be the same or very near the same as before. The capacitance nCi is obtained from the difference between the reading of ;LIz obtained from A-4.3.5(g) and the mean of the two The same procedure is carried out when the readings obtained from A-4.3.5(f). specimen has been removed. i-5. PROOF TEST FOR ELECTRIC STRENGTH A-5.1 Outline of the Method - Prescribed voltage is applied uniformly and rapidly to the electrodes, whose plane faces arc in contact with the test piocc, starting from zero and examined for any breakdown. A-5.2 Apparatus - The test voltage shall be provided by a trC~nsformer and shall be alternating of nominal frequency 50 11~. l'hey shall be of approxrmatcly sme wave form and the ratio of the peak value of the root mcarr square value shall be within the limit +`2 rfi 5 percent. `The output of 111e testirlg set shall be sufficient to maintain on the test piece the neccsnary voltage for the maximum time required. l'lre test voltage shall bc dctcrrnincd by means of a peak or other type of'voltmctcr comrected across a portion of the output winding. Any instrument used except the shall be calibrated against a peak voltmeter connected peak voltmeter ;tcross the output winding of the transformer. If there is any risk of the, current taken by the test piece altering the no load calibrating appreciably, calibration against a sphere gap shall bc made with a test piece in circuit. A-5.2.1 Electrodes-The lower electrode shall consist of a solid cylinder of brass 80 mm in diameter and approximately 25 mm thick and the upper electrode shall consist of a solid cylinder of brass 40 mm in diameter and not less than 40 mm thick, the plane faces of the electrode bt:iug in contact with the test piece and concentric with each other during `I'he sharp edges shall be removed from the electrode, the the test. radius at the edge being approximately 1 mm ( see Fig. 7 ). A-5.3 Procedure shall be tested. Test Pieces -"I'he test pieces shall be flat disc with smooth less than 100 mm in diamctcr and 3.2 5 0.2 mm it1 Incan The variation in thickness shall not cxcced 0.2 mm. A-5.3.0 Five test picccs A-5.3.1 surfzlces not thickness. A-5.3.1.1 Test pieces shall bc protected from light as compIetcly as possible during the interval bctween vulcanization and testing and care sllould bc taken to avoid handhng and contamination of the surface. 23 IS : 6693 - 1972 1R \t 40 8-s I I 40 TEST SPECIMEN I 1 lRMAX-//) BRASS , I 25 BRASS I lR,MAX I I I[ I_-----so0------J All dimensions Fm. in n~illimctrcs. 7 ARRANGEMENT OF ELECTRODES FOR ELECTRIC STRENGTH TEST A-5.3.1.2The test pieces shall be conditiourd at a temperature of 27 -& 2°C arlcl relative humidity of 65 5 5 percent, for not less than 18 hours immediately before test. A-5.3.2 Temperature of 27 -+ 2°C. ?f Test-The test shall be made at a temperature A-5.3.3 Place the test pieces concentrically, between the electrodes Commence and carry out the test under transformer and switch gear oil. the test as soon as possible after immersion of the test piece in oil. When raise the voltage applied to the electrodes as the test is commenced, rapidly as consisterit with avoiding transient over voltages from zero until Maintain the prescribed voltage for the prescribed voltage is reached. one minute. A-5.3.3.1 The electrodes shall be applied within 3 minutes `after The test shall removal of the test pieces from the controlled atmosphere. be started within 3 minutes after the application of the electrodes. A-5.3.4 Results - Individual the test if no breakdown occurs A-5.3.4.1 Not more the five samples tested. than to have before the end of this period. test pieces shall be deemed passed one of the samples shall fail the test out of 24 IS : 6693 - 1972 APPENDIX ( Clause 6.1 ) SAMPLING B-l. B-l.1 SCALE OF SAMPLING B OF EBONITE Lot - In any consignment all the pieces of ebonite manufactured by the same firm under sirnllar conditions of manufacture shall be separated in F;roups of 5 000 pieces of ebonite or less and each shxll constitute a lot. -1.2 Test for the determination of the conformity of the lot to the requireThe mcnts of this specification shall be carried out for each lot separately. nrlmber of pieces to bc selected for carryin,_ m out the test for dimr:nsional characteristics shall be in accordance with co1 1 and 2 of Table 5. TABLE NUMBER OF I'IEC~~S 5 SCALE OF SAMPLING TO RR ~`ERMISSIBLE NUMBER OF I)EFECTIVE (:1) 0 PIECES NIJMHER CIPPmxs SliLECTED (2) IN THE LOT (1) (,?f) (12) up to 500 8 501 to 1000 1 001 3001 )) 3000 ), 5000 13 32 50 1 1 2 B-1.3 The test pieces shall be selected at random (see IS : 49&j-1968* ). In order to ensure the randomness of selection, a random number table as agreed to between the purchaser and the supplier shall be used. In casr, such a table is not available, the following procedure shall be adopted: Starting from any piece in the lot, count them as 1, r and so on, in one order, where r is the integral part of the number of pieces in the lot and n the number of pieces Every rt.h piece thus cor~rltctcl shall IX withdrawn IO give test. B-2. 2, 3,......up to Jzrl,, Jv being in the sample. the sample fi,r TEST PIECES teats other than the tests for out by stalldard methods and the same: dq7rcc: 0f B-2.X For rods, tubes, and moulded sections, dimcusional characteristics shall bc carried OII sheet material of the same composition *Methods for random sampling. 25 IS : 6693 - 1972 vulcanization simultaneously B-3. NUMBER as the through OF which shall be processed material supplied, all the stages with each batch of production. TESTS characteristics shall be carried out on each B-3.1 Tests for dimensional of the pieces selected in B-l. B-3.2 Tests for the remaining characteristics shall be carried out preferably on test pieces taken from the sample in B-3.1, otherwise on the test At least one test shall be carried out for pieces supplied by the supplier. each of these requirements. B-4. CRITERIA FOR CONFORMITY B-4.1 Dimensional Requirements ~ The lot shall be considered to f01, dimensional c~haracteristics if tire ~nrrr~l~-~~ satisfy lhc requirement (see B-3.1 ) does not exceed the of defective picccs in the sample permissible number given in co1 3 of Table 5. A piece shall be COIIsidered as defective if it fails to satisfy any of lhe requirements for dimensions. B-4.2 Other Requirements ~ The lot shall be considered to satisfy the requirements for each of the characterislics other than the dirnensiorral if the test piece ( .tee B-3.2 ) satisfies the rcquircment for each d &se characteristics. B-4.2.1 If the test piece fails to comply with any specified test, two additional sets of test pieces shall be drawn and subjcctrd to that test. The lot shall be considered to satisfy the requirement if both the test pieces pass the test. B-4.3 The lot shall be considered to satisfy all the requirements specification if it passes in B-4.1 and B-4.2, otherwise not. of this 26 AMENDMENT IS 6693 : 1972 A-2. CROSS BREAKING A-2.1 Apparatus NO. 1 NOVEMBER 1998 TO SPECIFICATION FOR EBONITE the following for the existing: STRENGTH (Page 10, clause A-2) -Substitute A-2.1.1 Testing machine to apply a tensile force to the test piece via the grips and ronfomting to the following; rec!uircments: a) The applied force shall bc known to withm 1.5 percent of its true value, and A-2.1.2 Gips to hold the test piece in the test m ;:chiue b;4 chcrting a unli;~r~ir prrd:sure across the gripping surface, A-2.2 Test Pieces A-2.2.1 SIrape ati Dimensions Test piece shall be prepared having the shape and dimensions shown in Fig. 1. The test pieces may be punched or cut from sheet material. The material may be softened by heating to facilitate punching. The faces and sides of the test piece shall be machined to a smooth finish. A milling cutter of 50 mm radium cutting edge is suitable for shaping the narrow portion of the test piece. For any individual test, the width at any point on the narrow part of the dumb-bell shall not deviate by more thau 0.1 mm from the mean width, and the thickness at any point shall not deviate by more than 0.05 mm from the mean thickness. Three test picccs shall be tcstrd results on test pieces which break outside the uarrow section or which are obviously dcfcctive shall be discarded and retests made. Amend No. 1 to IS 6693 : 1972 A-2.3 Time-Lapse Between Vulcanization and Testing and A-2.3.1 For all test purposes the minimum time-lapse between vulcanization testing shall be 16 h. A-2.3.2 For product testing time lapse between vulcanization not exceed 3 months. A-2.4 Conditioning Test pieces should be conditioned for 3 hours. A-2.5 Temperature of Test 27 c 2*C. and testing shall All tests should be carried out at a temperature A-2.6 Procedure ne A-t.7 width of the test pieces shall be measured to within 0.2 mn~. l`estirrg Place rhe test piece with iLs wide face on the outer supports. Force to be applied by nouns l)f loading foot to act midway between the outer supports and perpcrrdicuiarly to the test piece, until failure occurs. The rate of movement nf the loading foot shall be 30 + 15 s to reach maximum load. Record the maximum force. S F I b u = cross breaking strength; = the maximum force, in Newton; = the distance between the fixed supports, in mm; = the width of the test piece, in mm; and = the thickness of Ihe lest piece, ii1 mm. strength of the three IN pieces shall be The medium value of the cross-breaking quoted as the cross-breaking strength. Amend A-2.9 Test Report No. 1 to IS 6693 : 1972 The test report shall include the following particulars: a) The cross-breaking b) The individual c) The temperature strength in meganewtons per square metre, values of cross-breaking of the test, and strength of the three test piece, d) The time interval between vulcanization and testing. (PCD13 )